1. Field of the Invention
The invention relates to sediment barriers which are installed in stormwater run-off ditches to control erosion and sediment run-off into to natural watercourses. More particularly, the invention relates to such barriers as are commonly used on highway construction projects while land is being disturbed as by grading, clearing or excavating and the like. The ditch check in accordance with the invention partly dams up and slackens the stormwater run-off in the ditch, to promote the accumulation of sediment before the ditch check.
2. Prior Art
Ditch checks are required by some states as temporary erosion and sediment control measures during highway construction. Ditch checks are part of a larger integrated plan to prevent stormwater run-off from carrying into natural watercourses sediment from any land disturbed by construction. Generally, the ditch checks are required to remain in place until seeding and mulching operations protect the disturbed land such from erosion.
The requirement for ditch checks originates in the Federal Clean Water Act, 35 U.S.C. 1251 et seq., and devolves through several tiers of federal and state laws and regulations, to appear by name in state-administered permit programs. This happens as follows. The Federal Clean Water Act includes a program denominated as the National Pollutant Discharge Elimination System (NPDES), 33 U.S.C. 1342, for which is established minimum criteria and standards that appear in 40 C.F.R. 125.1 et seq. The NPDES criteria and standards are policed via permit programs, some which are administered federally by the Environmental Protection Agency--i.e., 40 C.F.R. 122.1 et seq.--and others whose administration is delegated to the states, 40 C.F.R. 123.1 et seq. Construction activities as clearing, grading and/or excavation which disturb five or more acres of land, require permits. 40 C.F.R. 122.26(b)(14)(x).
Missouri, for example, has enacted its NPDES permit program into its Clean Water Law, RSMo 644.006 et seq., and, RSMo 644.051.1(3). Missouri has an executive department, the Department of Natural Resources, that is given the authority to "issue . . . permits in order to enforce the Missouri Clean Water Law and regulations and administer the NPDES." MoCSR, Title 10, 20-6.010(1)(A). Stormwater run off is specifically addressed in MoCSR, Title 10, 20-6.200.
There are two kinds of permits, an individual permit and a general permit. The state highway system is approved for coverage by general permits where appropriate. MoCSR, Title 10, 20-6.200(5)(A)1.C. And where not appropriate, an individual permit must be secured via an application for a "land disturbance" activity. Both kinds of permits are alike in requiring narrative descriptions of proposed "best management practices (BMPs)," wherein "best management practices" for land disturbance is a defined phrase, which definition includes but is not limited to "sediment (silt) fence and staked straw bale barriers." MoCSR, Title 10, 20-6.200(1)(C)2.E.
A general permit for the state highway system has been granted to the Missouri Highway & Transportation Department (MoDHT). The MoHTD has an internal Design Manual which states the following, at section 4-09.5(2), last revised May 15, 1995. A temporary erosion and sediment control plan is required for all projects that disturb any land area. The purpose is to prevent the sediment that results from the contractor's activities from leaving the right of way, and intercept it before it enters crossroad drainage. Generic erosion control plans are available as "special sheets." At section 4-09.5(2)(c), the MoHTD Design Manual addresses ditch checks as follows. Ditch checks are used to contain sediment on the construction site, and there are three types. "Silt fence ditch checks" may be used for drainage areas of less than two acres. "Rock ditch checks" should be limited to ditches with grades of 4% or less. And "straw bale ditch checks" may be used in small ditches with grades of 2% and less.
The above-mentioned "special sheets" depict an exemplary straw bale ditch check 10 as shown herein by FIGS. 1, 2 and 3; as well as an exemplary rock ditch check 12 as shown by FIG. 4, and an exemplary silt fence ditch check 14, as FIG. 5 shows.
The MoHTD also has an internal design specification entitled "Temporary Erosion and Sediment Control DSP-93-05A." The special sheets and the design specification, if taken together, state the following regarding the use and maintenance of the different types of ditch checks.
FIG. 1 shows four bales of straw 20 installed in a ditch 22. Arrow F indicates a downstream direction of the stormwater run-off. Each bale 20 is anchored by stakes 24. The bales 20 are mashed together to minimize gaps therebetween, and are lashed together by wires 26. Loose straw 28 is wedged in the gaps to fill them. Whereas a geo-textile fabric 30 is optionally stapled to the bales 20, it is omitted for slopes of 2% or less, which is usually the case. The spacing between straw bale ditch checks 10 for slopes of 2% is every 100 feet (30 m) along the centerline of the ditch (not shown). The outer ends of the ditch check 10 are preferably higher than the middle to insure flow through or over the ditch check 10, and not around it. The purpose is to obstruct the flow of water and allow the deposit of sediment on the upstream side.
The stated maintenance program for straw bale ditch checks includes removal of sediment deposits after each storm event. Also, sediment deposits must be removed when they reach approximately one-half the height of the barrier. The straw bale ditch check is maintained for the duration of time that the upstream land area is disturbed, and afterwards until seeding and mulching operations produce sufficient ground cover to protect the disturbed area from erosion.
As shown by FIG. 4, a rock ditch check 12 is created from 2 inch.times.3 inch (5.1 cm.times.7.6 cm) clean gravel 32, wherein 100% passes through a 3 inch grate and 95% is retained on a 2 inch grate. The gravel 32 is sloped on both the upstream and downstream surfaces 34 at a 2 to 1 slope. The height at the middle is limited to 2 feet (61 cm), and the outer lateral edges are approximately 6 inches (15 cm) higher in elevation to insure flow through and over the gravel barrier 12, but not around. The rock ditch check 12 shall be checked for sediment accumulation after each significant rainfall. Sediment shall be removed when it reaches one-half of the original height or before. Regular inspections shall insure that the center of the rock ditch check is lower than the edges. Erosion caused by high flows around the edges shall be corrected immediately. The rock ditch check shall remain in place until ground cover has sufficiently protected the relevant disturbed areas. After removal, the area beneath the rock ditch check shall be seeded and mulched immediately.
In FIG. 5, a silt fence ditch check 14 is shown installed across a ditch. The minimum height is 25 inches (64 cm) at the center. The fence 14 is supported by steel T-posts 36 or equivalents, at no more than 5 foot (1.5 m) spacing. The bottom of the ditch is trenched, and the fabric 38 is folded into the trench 40 and covered to a depth of between 6 and 12 inches (15 and 30 cm). Closer spacing, greater embedment depth and/or wider posts are used as necessary to insure adequate resistance to applied loads. A typical fabric is disclosed by U.S. Pat. No. 5,108,224--Cabaniss et al. The silt fence ditch check 14 shall be inspected immediately after each rainfall and at least daily during prolonged rainfall. Sediment shall be removed if the deposit approaches one-half the height of the fence, or else sooner. If required by heavy sediment loading in the fabric, a second silt fence shall be installed.
The foregoing thus details the different uses, maintenance schedules and inspection routines of the three varieties of ditch checks. Straw bale ditch checks are very common on highway construction projects. And with spacing typically at 100 feet (30 m) between straw bale ditch checks, a typical highway construction project deploys hundreds of them.
There are, however, shortcomings with the use and maintenance of straw bale ditch checks. In Missouri, contractors bid on average between $55.00 and $100.00 per installed ditch check. Whereas the materials used in the ditch check are economical, the installation, maintenance and repair is relatively costly. Dry bales of straw are relatively heavy and bulky, and require costly storage, transportation to the construction site, and labor in the field to accomplish installation in the mass quantities required.
In use, a straw bale ditch check is supposed to partly filter the water as well as obstruct it. However, the bales become waterlogged in a ditch carrying stormwater run-off, and load up beyond any capacity to filter. Thereafter, water runs over or around the edges of the bales of straw. When water runs around the edges of the straw, it promotes rather than inhibits erosion.
Experience discloses that, in a big rainfall, about three-fourths of the stormwater run-off finds its way around the edges, and no or little sediment is deposited in front. Repair of waterlogged bales of straw requires replacement. Then, the bales of wet straw weigh between 125 and 150 pounds if they can be removed as an entire piece. Usually, however, they bust up under their own weight, and require substantially more valuable time of workers to remove them and reinstall their replacements. It has happened that, during a six to eight month construction project, the straw bale ditch checks have had to been replaced five to six times.
Even when the straw bale ditch checks work as planned, and cause the sediment to deposit in front, the clearing away of the sediment deposit as required often results in damage to the bales by spades or machinery and the like.
What is needed is an improvement which overcomes the shortcomings associated with straw bale ditch checks.